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How are photon energy and frequency related in spectroscopy?

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In spectroscopy, the energy of a photon is directly proportional to its frequency. This relationship is expressed by the equation:

$E = h ν$

In this formula:
* $E$ represents the energy of the photon.123
* $h$ is Planck’s constant, a fundamental physical constant with a value of approximately $6.626 \times 10^{- 34}$ joule seconds.13
* $ν$ (the Greek letter nu) represents the frequency of the radiation.14

Because of this relationship, spectroscopy—which measures the interaction of photons with matter—is effectively a study of these interactions as a function of photon energy. By measuring the frequency of light absorbed or emitted by atoms or molecules, scientists can determine the specific energy levels of those systems, as the energy of the emitted or absorbed photon corresponds to the difference between two quantum states.23